GRIB format

GRIB (GRIdded Binary or General Regularly-distributed Information in Binary form) is a concise data format commonly used in meteorology to store historical and forecast weather data. It is standardized by the World Meteorological Organization's Commission for Basic Systems, known under number GRIB FM 92-IX, described in WMO Manual on Codes No.306.

Currently there are three versions of GRIB.

1. Version 0 was used to a limited extent by projects such as TOGA, and is no longer in operational use. 
2. The first edition (current sub-version is 2) is used operationally worldwide by most meteorological centers, for Numerical Weather Prediction output (NWP). 
3. A newer generation has been introduced, known as GRIB second edition, and data is slowly changing over to this format. Some of the second-generation GRIB are used for derived product distributed in Eumetcast of Meteosat Second Generation. Another example is the NAM (North American Mesoscale) model.

File Format

GRIB files are a collection of self-contained records of 2D data, and the individual records stand alone as meaningful data, with no references to other records or to an overall schema. So collections of GRIB records can be appended to each other or the records separated.

Each GRIB record has two components - the part that describes the record (the header), and the actual binary data itself. The data in GRIB-1 are typically converted to integers using scale and offset, and then bit-packed. GRIB-2 also has the possibility of compression.

GRIB superseded the Aeronautical Data Format (ADF).

The World Meteorological Organization (WMO) Commission for Basic Systems (CBS) met in 1985 to create the GRIB (GRIdded Binary) format. The WGDM in February 1994, after major changes, approved revision 1 of the GRIB format. GRIB Edition 2 format was approved in 2003 at Geneva.

Problems with GRIB

No way in GRIB to describe a collection of GRIB records

• Each record is independent, with no way to reference the GRIB writer's intended schema
• No foolproof way to combine records into the multidimensional arrays from which they were derived.

The use of external tables to describe the meaning of the data.

• No authoritative place for centers to publish their local tables.
• Inconsistent and incorrect methods of versioning local tables.
• No machine-readable versions of the WMO tables (now available for GRIB-2, but not GRIB-1)

GRIB 1 Header

There are 2 parts of the GRIB 1 header - one mandatory (Product Definition Section - PDS) and one optional (Grid Description Section - GDS). The PDS describes who created the data (the research/operation center), the involved numerical model/process - can be NWP or GCM, the data that is actually stored (such as wind, temperature, ozone concentration etc.), units of the data (meters, pressure etc.), vertical system of the data (constant height, constant pressure, constant potential temperature), and the time stamp.
If a description of the spatial organization of the data is needed, the GDS must be included as well. This information includes spectral (harmonics of divergence and vorticity) vs gridded data (Gaussian, X-Y grid), horizontal resolution, and the location of the origin.